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3.59 Where a single common discharge pipe serves more than one system, it should be at least
one pipe size larger than the largest individual discharge pipe (D2) to be connected.
3.60 The discharge pipe should not be connected to a soil discharge stack unless it can be
demonstrated that the soil discharge stack is capable of safely withstanding temperatures of the
water discharged, in which case, it should:
a. contain a mechanical seal, not incorporating a water trap, which allows water into the
branch pipe without allowing foul air from the drain to be ventilated through the tundish;
b. be a separate branch pipe with no sanitary appliances connected to it;
c. if plastic pipes are used as branch pipes carrying discharge from a safety device, they
should be either polybutalene (PB) or cross-linked polyethylene (PE-X) complying with
national standards such as Class S or BS 7291-2:2006 or Class S of BS 7291-3:2006
respectively; and
d. be continuously marked with a warning that no sanitary appliances be connected to the
pipe.
Notes:
1. Plastic pipes should be joined and assembled with fittings appropriate to the circumstances
in which they are used as set out in BS EN ISO 1043-1:2002.
2. Where pipes cannot be connected to the stack it may be possible to route a dedicated pipe
alongside or in close proximity to the discharge stack.
Termination of Discharge Pipe
3.61 The discharge pipe (D2) from the tundish should terminate in a safe place where there is
no risk to persons in the vicinity of the discharge.
3.62 Examples of acceptable discharge arrangement are:
a. to a trapped gully with the end of the pipe below a fixed grating and above the water seal;
b. downward discharges at low level; i.e. up to 100mm above external surfaces such as car
parks, hard standings, grassed areas, etc. are acceptable providing that a wire cage or
similar guard is positioned to prevent contact, whilst maintaining visibility; and,
c. discharges at high level: e.g. into a metal hopper and metal downpipe with the end of the
discharge pipe clearly visible or onto a roof capable of withstanding the temperature
discharges of water and 3m from any plastic guttering system that would collect such
discharges.
3.63 The discharge would consist of high temperature water and steam. Asphalt, roofing felt
and non-metallic rainwater goods may be damaged by such discharges.
The discharge pipe within the building is to be located within a frost free environment.
